Standpipe 1

[fireprotect]

I am assigned a class ii standpipe design for an existing 3 story residential building which 4th story is being added. Existing 3 story building has a 2” riser ( one 1 ½” Fire hose on each floor). Boiler room and garbage room in the basement is sprinklered (6 sprinkler heads total). system is served from 2” incoming city water without any pump or FDC. (a 3 story building does not require standpipe system according to code)
City water test result is: 58 psi static and 54 psi @1200 gpm. We require a fire pump since required pressure at 1 ½” fire hose is min.65 psi and max 100 psi.

My first question is should I count 50 gpm for most remote Fire hose and 100 gpm for the riser , or I just go with 100 gpm for remote fire hose?

2nd Q: Currently sprinklers are connected to existing 2” riser in the basement. If I don’t change this piping then my pump will serve fire hoses (6 FHC) and 6 sprinkler heads in the basement should I size my pump for 100 gpm or should I add sprinklers flow too? Maybe I can just connect sprinklers to header before pump since city pressure is enough for 8 sprinklers in the basement and connect FDC to after pump and after sprinkler control valve.